A hybrid vehicle and an electric vehicle (EV) are gathering attention due to a steep rise in the prices of fossil fuels. In particular, an EV with an in-wheel type axial gap motor built inside the wheel requires no intricate and heavy-weight transmission, contributing effective utilization of space, cost reduction, and weight reduction. As a vehicle that can use such in-wheel type axial gap motor, a 1-seater or 2-seater compact car intended for short-distance travel, also referred to as city commuter, has been gathering attention. Since high performance is required in the in-wheel type driving motor used in the EV vehicle, including the city commuter, rare-earth magnets using expensive rare-earth elements have been used so far.
However, prices of rare earth elements have witnessed steep rise in recent times, and it has become difficult to procure the rare earth elements. Therefore, an in-wheel motor for EV that uses a ferrite magnet, which is cheaper and easily available, is being considered for use instead of the rare-earth magnet. Since the residual magnetic flux density of ferrite magnet is approximately 30% lower as compared to the rare-earth magnet, decrease in torque is at issue. In order to solve this issue; (1) an axial gap motor type structure was employed with an expectation for increase in torque and thinning in the axial direction, (2) permanent magnets (SPM) were mounted inside a rotor of this structure for maximizing torque and reducing iron loss inside a stator core; (3) further, a prototype of 5 kW size motor structure with a reduction gear installed inside a stator was manufactured in order to effectively utilize space inside the motor, and acute experimentation and research were repeated on the operating characteristics thereof. When a prototype of 10 kW size motor (16 poles and 18 slots) was manufactured for further increasing output, and operating characteristics thereof were measured, a problem of increase in eddy current loss inside the rotor was ascertained, while this problem was not apparent in the 5 kW size motor structure.
Therefore, the present invention has been made in order to solve the above-described problem, and the object of the present invention is to provide an electric motor, especially an axial gap motor, with little eddy current loss.